With reference to FIG. 1, when a flat wire conveyor belt 10 is used in a spiral system or turn, tension is carried on the outer edge 12 of belt 10 by reinforcing bars 14. The wickets 16 on belt 10 are for product support, rather than taking a load, and the rods 18 are utilized to hold the components of belt 10 together, and to transmit drive forces to the outside edge 12 of belt 10.
In a straight run, such as the infeed and discharge areas of a spiral system, the outer reinforcing bars 14 have little if any effect on the function of belt 10. A sprocket 20 tooth, which engages rods in a straight transport course downstream of a course turn, causes rod 18 to deflect at sprocket 20, releasing tension from the outside edge 12 of belt 10. This causes wickets 16, whose purpose is for product support, to now take the tension of the belt 10. The sprocket-engagement area 22 of rod 18 takes tension from sprocket 20 and applies it to adjacent wicket areas 24 to cause wicket fatigue and breakage at one or more of wicket areas 24 where rod 18 meets wickets 16.
Fatigue breakage at one or more of wicket areas 24 of a flat wire conveyor belt is a function of the number of cycles that a particular area 24 is flexed. Failure of a wicket can be accelerated by adding tension thereto. Two areas where a flat wire conveyor belt such as shown in FIG. 1 has the most tension is on the outer edge 12 of belt 10 and in the sprocket-engagement area 22 of belt 10. When rod 18 flexes to distribute the tension or load, wicket 16 also is flexed until tension is transferred from the edge 12 to the engagement location of sprocket 20. Thus, it is believed that such flexing causes wicket breakage.
The use of reinforcing bars 14 on the outer edge of the conveyor belt is not entirely successful in eliminating fatigue failures on the outer edge 12. Accordingly, further design improvements have been made, such as described in U.S. Pat. No. 5,934,448 assigned to Cambridge International, Inc., the contents of which are hereby incorporated by reference. According to one preferred embodiment of the '448 patent, a split between the links is formed in each row of wickets, and a tension link is positioned within each split therebetween. The tension links are formed of heavier gauge material than the material from which the wickets are formed, and preferably have a thickness which is about two to about four times thicker than the wicket thickness. Each tension link is a generally U-shaped member, wherein a base portion of the U-shaped tension link contacts one rod, and two leg portions of the U-shaped tension link contact an adjacent rod in the succession of rods. The tension links can also be between pairs of reinforcing bars.
While the conveyor belt of the '448 patent exhibits outstanding performance and has enjoyed substantial commercial success, the use of heavier gauge material for the tension links substantially increases the overall costs of manufacturing the belt. Accordingly, there exists a need in the marketplace for a flat wire conveyor belt having a lighter weight and reduced quantity of required material; thus reducing the cost, while still retaining its strength in a turn configuration.